WO1996004776A1 - Crop strippers and stripper toothing - Google Patents

Abstract

A crop stripper has a rotary drum with rows of stripper teeth (14) formed by toothing elements (10) made of sheet metal and having an essentially continuous rearward flange (18) running around the edges of the profile of the teeth. Radially inwards of the teeth the toothing elements have a flexible inner margin (22) to allow the teeth to yield when they strike an obstacle. The toothing elements have slots (38) open to their radially inner edges to be slidable onto clamping bolts (30) while the bolts remain in place on the drum. Locking projections and recesses (40, 42) between the toothing elements and their clamping faces secure the elements positively when the clamping means is tightened.

Description

CROP STRIPPERS AND STRIPPER TOOTHING!

This invention relates to crop strippers and the rotary drums of such strippers used for detaching crops to be harvested from standing plants . Such crop strippers are best known for stripping grain from the heads of cereal crops such as wheat, and seed from herbage crops such as grass, but they can also be arranged to harvest other grain or seed crops, or to strip leaves, young shoots or blossom, for example, from the stems of crops.

The drums of crop strippers are provided at the periphery with stripper teeth arranged in a series of axial rows or combs each made up of a number of similar comb plates butted end to end. As the machine advances through the standing plants the drum is rotated with its lower periphery turning in the direction of advance and the plant stems are trapped in the spaces between the projecting teeth. As the stems are drawn around the drum by the teeth the grain or other crop is stripped from the stems.

For efficient operation the teeth of the stripper drum should not remove significant quantities of unwanted parts of the plants, in particular the stems, because that can interfere with the collection of crop that is being collected, and because they must subsequently be separated to be discarded. The efficiency of operation in this respect is dependent, to some extent at least, on an ability of the stripper teeth to yield to the resistance of the plant stems through which they are drawn. It is also necessary for the teeth to be able to yield to avoid damage when they strike obstacles on the ground.

To meet these requirements it is customary to make the comb plates of a thermoplastic material, which provides a high degree of flexibility and also causes little if any damage to the crop stems because it is a relatively soft material. This latter property, however, means that the teeth wear very rapidly in some crops and require frequent replacement. Although they are known to be considerably more wear resistant, metal teeth have not been employed in practice because of the damage they do to the crop stems and their liability to be damaged by accidental impact on account of their greater stiffness.

In a stripper drum, according to a first aspect of the present invention, however, metal toothing elements are provided, each having a plurality of teeth, the tooth profile comprising a radially outwardly tapering portion and a root portion inwardly of said tapering portion where the spacing between adjacent teeth increases to form a root opening with a maximum width greater than a radially outer neck of said opening, the teeth having an essentially continuous rearward flange running along the edges of the said profile including said root portions, and said toothing elements being arranged to be flexibly yieldable circumferentially of the drum.

Preferably said rearward flange is formed with an essentially constant radius junction between it and a main body of the toothing element from which it extends. The flanged formation of the tooth profile allows the toothing elements to be produced from a relatively thin sheet metal but is able to avoid, or at least substantially reduce, the damage to crops that stripper teeth of such a material have previously caused. Although the provision of such a continuous flange would be regarded as undesirable because of the resulting increase of stiffness, it is possible to provide a required degree of flexibility through the mountings of the toothing elements, or preferably by arranging that a portion of each toothing element radially inwards of the teeth themselves to have sufficient flexibility.

It has been found that a toothing element made of sheet metal, in particular of spring steel, can be arranged to be yieldable circumferentially to a sufficient degree by allowing the elements to flex in a region between said tooth roots and a radially innermost edge portion by means of which the element is secured to its drum. Said main body may conveniently be planar, but if required, the flexibility of said region can be enhanced by at least one corrugation extending generally parallel to the rotary axis of the drum and/or one or more apertures in this region of the element. It is usually desirable to keep the radius of curvature of the edge profile small to promote efficient stripping action, but the limits of ductility of the tooth material may dictate the minimum radius of curvature. In that case, the radius of curvature is proportional to the thickness of the material and is thus also related to the tooth stiffness. This can make it difficult to obtain optimum values for both the radius of curvature of the tooth edge profile and tooth stiffness. It is possible to overcome this problem by providing one or more backing elements at the rear of a toothing element having the flanged edge profile, the or each said backing element having at least one tooth-like projection with a profile that lies within the edge profile of a tooth of its associated toothing element.

In this way, the stiffness of the toothing elements can be increased without affecting the tooth edge profile in circumstances in which the adoption of a thicker material for the toothing element would otherwise result in too large a radius of curvature on that edge profile. The backing elements can be of a similar material to the toothing elements, in particular a sheet metal such as spring steel . Depending upon the degree of stiffening required they can be of the same or of a different thickness sheet to that of the toothing elements and they can be placed in multiple layers behind the toothing element.

A stripper drum will usually have a series of toothing elements according to the invention jointed end to end in the or each row of stripping teeth, because of the overall length of the drum. Where this is done a guard strip is preferably placed in front of the elements of each row of teeth in order to shield the junctions between adjacent elements. Although it is possible to butt the elements closely together, as individual elements are flexed under load, gaps can appear between their abutted edges and in some circumstances there is a risk that crop parts will become jammed in these gaps and interfere with the operation of the stripper drum. The guard strip provides a shield against the entry of foreign matter between the joint edges.

If backing elements are provided for the toothing, these can be utilized alternatively or additionally to a front guard strip to protect joints between successive toothing elements from trapping excessive amounts of foreign matter and/or to lock the toothing elements in place. Reference has been made to the need to be able to replace the stripper teeth. It will be understood that because of the length of a typical stripper drum and the need to secure the toothing elements firmly, typically by screw bolts, against displacement by both centrifugal force and the resistance of the crop through which the teeth move, it can take a very considerable time to change the stripper teeth. Even though the use of metal teeth in accordance with the present invention as set out above increases the intervals between such changes, it would be desirable to improve operational efficiency further by reducing the time to make a change. According to another aspect of the present invention, there is provided a toothing element for a crop stripper drum having a radially innermost base portion to be held between opposed support faces of the drum by releasable clamping means passing through the base portion and said support faces, the base portion of the element being provided with at least one slot opening into a radially innermost edge of the element to receive said clamping means by sliding the element base portion between said opposed support faces while the clamping means are in position in said faces, and at least one locking device, said device or devices of the toothing element being one of cooperating recess and projection elements provided in the toothing element and said support faces respectively for locking the element positively in the radial direction when it is gripped between said faces by the clamping means. Where guard strips are provided, as described above, that strip can also be provided with elements of said locking devices to hold the toothing elements in place.

With such an arrangement, it can be arranged that by loosening the clamping means it is possible to give the toothing element sufficient freedom of movement between said support faces to release the locking devices. Because the toothing element can then be slid from the clamping means it is possible to leave those clamping means in position, although loosened, while the toothing element is being replaced.

If the toothing element is of sheet metal, its locking device element or elements can conveniently be bent out from the sheet in the form of a tongue or tongues. It is to be understood, however, that in this aspect the invention is also applicable to toothing elements of other materials such as plastics, with which the locking devices may be more conveniently formed in other ways.

Preferably, that element of the or each said cooperating device which is on a toothing element to be located at end edges of the toothing element. If for example the projections of said cooperating devices are adjacent the abutting faces of successive toothing elements they can be located in a common recess in the margins of both elements adjoining said abutting faces, so simplifying the production of the support face having the recesses.

It has also been found desirable to form the projections and/or slots with radiused ends, so as to limit the concentration of stresses at their ends from the loading applied by the toothing elements. If the toothing element is associated with a guard strip and/or backing element as referred to above, the locking devices may comprise an element or elements on said strip and/or backing element for cooperation with a complementary formation on the toothing element.

For speed of replacement, the toothing element may be arranged to be clamped by a single clamping member centrally of its length with one or more locking devices to each side of the clamping element and spaced therefrom.

By way of example, the invention will be described in more detail with reference to the accompanying schematic drawings, in which: Fig. 1 is a radial section of a crop stripper drum,

Fig. 2 illustrates to a larger scale the area circled in Fig. 1,

Fig. 3 is a rear view on a series of comb plates sections and their guard plate,

Fig. 4 is a larger scale sectional view of line IV-IV in Fig. 3.

Fig. 5 is a rear view of a backing element for a stripper drum with some of its associated toothing elements, and also illustrates a modification of those elements,

Fig. 6 is a radial section of a crop stripper drum showing the assembly of toothing and backing elements of Fig. 5 on the drum, Fig. 7 is a larger scale illustration of the circled area in Fig. 6, and

Fig. 8 is a sectional view on the line A-A in Fig. 5. Fig. 1 illustrates diagrammatically the construction of the outer shell of a stripper rotor drum which is supported on a central rotary shaft (not shown) to rotate in the arrowed direction. The shell comprises a series of axially extending cover plates 2 which form the peripheral surface of the drum body. Each cover plate is a Z-section member with a main web 4 generally tangential to the rotary axis and from the leading and trailing edges of which project a pair of generally radial wings 6,8. The wing 6 at the leading edge of the web. is directed outwards and the trailing edge wing 8 is directed inwards.

The wings 6,8 of adjacent cover plates 2 lie parallel to each other at a small spacing apart. In the space between each said pair of wings toothed comb plates 10 and guard strips 12 are inserted, the comb plates and the guard strips both being mounted in end-to-end series extending along the length of the drum. Each comb plate is pressed from a thin (0.6 mm) spring steel plate. It is given a comb profile of a generally conventional form comprising a series of tapering teeth 14 with bulbous openings 16 between the tooth roots. In the pressing operation, the profile is formed with a small rearwardly directed flange 18 that extends continuously along the toothed profile, including the bulbous root openings 16. The inside radius at the root of the flange is preferably not substantially more than three times the metal thickness. The height of the flange is preferably not substantially less than 4 mm, measured from the front face of the tooth.

The flange 18 increases the stiffness of the comb plate 10 over the height of the tooth profile but the inner margin 22 of the plate between the profile 14,16 and the shorter wing 6 behind the comb plate remains planar and the thin spring steel has considerable flexibility in the circumferential direction of the rotor drum. In use, therefore, with the drum rotating in the arrowed direction, a comb plate can deflect rearwards if it strikes an obstacle on the ground, as a result of the flexibility of the inner margin 22. If additional flexibility is needed, the inner margin 22 of the toothing element can be given one or more corrugations 24 or a series of apertures 24a. Preferably the radially outer edge of the wing 6 is radiused rearwards to spread its loading on the flexed comb plate.

The arrangement offers several advantages compared with conventional comb plates of plastics. These relatively soft and flexible materials have been used because they do little damage to the standing plants and because they flex easily if they strike obstacles, such as stones. The spring steel comb plate has a much longer operational life because of the resistance of the metal to abrasion. The flanged edges of the comb profile present a smooth face to the crop and are found to be surprisingly effective in reducing the potential for crop damage that has hitherto made the use of metal comb plates impractical for many crops. The stiffening of the individual teeth of the comb plate by the flanged formation could make them vulnerable to damage from stray impacts, but it is found the comb plate can still be made sufficiently flexible to avoid this defect by a suitable choice of sheet metal and the manner of support over its inner margin. The ability to manufacture the comb plates as simple pressings keeps their cost down.

The axial length of stripper drums is typically several metres and as a practical matter each row of teeth is made up from a number of short, usually identical, comb plates, as is illustrated in Fig. 3. Although the edges of the plates can be butted closely to each other to form an essentially continuous face, if one section is subjected to a greater load than its neighbour, eg. because its teeth have struck an isolated obstacle such as a large stone, a gap opens momentarily between the edges of the adjacent sections. There is then a risk that parts of the crop will lodge in the gap and be trapped when the section springs back, so leaving the gap open. There can then be a progressive build-up of material trapped in the gap, to the extent that the operation of the stripper is disrupted.

To counter this risk, the guard strip 12 is sandwiched between the front face of the comb plates 10 and the trailing wing 6 of the cover plate. The guard strip 12 extends over the inner margin of the comb plates, its outer edge lying at the same radius from the drum centre as the bulbous root openings. The guard strip therefore does not alter the active or stripping profile of comb plate but merely overlies the butt joints between comb plates at the centres of the root openings. That is sufficient for it to be able to cover the gaps that will open from time to time between the comb plates. To fulfil this function the guard strip can be of a softer and thinner material than the comb plate itself, but is preferably also of metal. Although the comb plates described have the potential for a long operational life, it is necessary to replace the plates from time to time. However, because of the high loadings they experience, both from centrifugal forces and from the resistance of the crop through which they move, they must be locked firmly in place. For these reasons, comb plates are conventionally provided with a number of holes for screw bolts by means of which they are located and clamped between the drum cover plate wings. To replace a comb plate, therefore, the bolts securing it are first removed from the drum to allow the damaged plate to be slipped out, a new plate is put in place and its bolt holes registered with the bolt holes in the cover plate wings, and finally the bolts are reinserted and re-attached to their captive nuts and tightened. This procedure can result in considerable downtime, particularly if it must be repeated with a number of comb plates.

In the illustrated example, the attachment of each comb plate to the drum is obtained using a single bolt 30 which extends through holes 32,34 in the opposed wings 6,8 and similar holes 36 the guard plate but through a central open slot 38 in the each comb plate, the slot extending to the inner edge of the plate. To each side of the central slot 38 the plate also has a pair of tabs 40 formed by U-shaped cuts and pressed out from the spring steel plate about a radially inner bending line. The guard strip 12 is provided with a further series of holes 42 of a complementary profile in which the tabs 40 can be located.

When the stripper drum is fully assembled, the sprung-up outer edges of the tabs 40 seat against the outer edges of the guard strip holes 42. The comb plates are thereby held positively against movement radially outwards of the guard strip 12 which is in turn held positively against such movement on the stripper drum by the bolts 30 passing through the holes 42 in the strip. The central bolts clamp the comb plates tight between the two wings 6,8 to complete the attachment in a manner which precludes any displacement of the comb plate relative to the drum.

When a comb plate 10 is to be replaced, its bolt 30 does not have to be removed. The bolt is merely loosened on captive nut 44 sufficiently to allow the comb plate to be eased back to release the tabs 40 from the locating holes 42 in the guard strip. Because the bolt 30 passes through the open slot 38, it is possible then to slide the comb plate out from between the wings 6,8 and slide in a new comb plate. It then remains only to tighten the nut on the bolt, which has remained attached to the drum cover plates throughout. It will be understood that a similar means of attachment can be provided for comb plates made of thermoplastics or other materials to facilitate their replacement.

It will also be understood that the comb plates may have holes or recesses engaged by projections in the co-operating locking parts, instead of the tabs that seat in holes or recesses in those parts.

In the modification shown in Fig. 5, a backing element 52 is provided in the form of an elongate strip having a series of similar projections 54 at the same pitch as the teeth 56 of a number of toothing elements 58 with which it is associated. The projections 54 are, however, narrower and shorter than the teeth 56, and the recesses 60 between them are slightly deeper than the recesses 62 between the teeth, • so that they fit within the profile of the toothing elements as defined by the flanging 64 that extends continuously along the profiled edges of the teeth.

The stripper drum 70 is constructed using a series of cover plates 72 in the manner described in the first embodiment. At equally spaced positions around its periphery groups of toothing elements 58 form rows of stripper teeth along the length of the drum as before but now groups of backing elements 52 also extend the length of the drum behind the rows of teeth.

In the base region of each backing element 52 a series of holes 74 are provided to receive bolts 76 securing the elements in place on the stripper drum. Alternating with the holes 76 are elongate slots 78 at the same pitch as the I'ength of the toothing elements 58. These slots have an elongate rectangular form with rounded corners. The toothing elements 58 are essentially similar to those described in the first embodiment but locking tabs 82 replacing the tabs 40 are pressed out from the element at its opposite ends rather than intermediate the length of the element. Fig. 5 illustrates how adjoining tabs 82 of two succeeding toothing elements locate in a common slot 78 in the backing element. Radially outwards from each tab 82 the edge of the toothing element can have a radiused indent 84 to improve the stress distribution under flexure. As in the first example, the toothing elements also have slots 86 which are coincident with the bolt holes 74 and which open into the radially inner edges of the elements. As can be seen from Fig. 6 and 7, the toothing and backing elements are clamped between wings of the Z- section cover plates 72 of the rotor drum by the bolts 76. The backing elements 52 are located radially and axially by the bolts 76 passing through their bolt holes 74. The bolts 76 also engages the slots 86 of the toothing elements 58 to locate those elements axially but positive radial location of the toothing elements is provided by the tabs seating in the backing element slots. Removal and insertion of the toothing elements can be carried out in the manner already described, when the bolts 76 are slackened off.

It will be noted that the backing elements 52, which are considerably longer than the toothing elements 58, are so arranged that their butted ends do not coincide with the butting joints between successive toothing elements. Should one of the toothing elements flex rearwards more than its neighbour, eg. because it has struck an obstacle, because the joint between the two elements is bridged by the associated backing element, there is less tendency for a gap to open between them and any such gap has the backing element overlying it. If it is necessary to provide .some protection against the entry and trapping of foreign matter when such gaps develop, therefore, the backing elements may replace the guard strips 12.

Depending upon the conditions of use of the stripper drum, it may be desirable to have both the backing elements and the front guard strips performing this shielding function or to rely solely on front guard strips as in the first embodiment described. Similarly, it is possible to arrange that the location of the toothing elements is shared by the backing elements and guard strips or is obtained by a front guard strip alone. The backing elements 52 allow a greater choice of stiffness for the toothing elements independently of the material and form of the toothing elements 58. They do not have to be made of the same material as the toothing elements. Also, although the example shows a single backing element as the rear support for each stripping finger, it is possible to provide backing elements in multiple layers, possibly of different radial dimensions, to provide further choice in the stiffness characteristics of the drum toothing. For example, backing elements with longer projections 54 can themselves be backed by elements with shorter projections so that they have the combined effect of raising the stiffness increasingly towards the radially inner ends of the toothing.

It is also possible to reduce the stiffness of the radially inner regions of the backing elements if this is required to give the toothing a required ability to deflect, eg. by use of apertures or corrugations in this region, as has already been described for the toothing elements.

Fig. 5 also illustrates a modification of the toothing elements, shown in more detail in Fig. 8, in which the flange 64 along the profiled edge is interrupted at the angular transitions 88 between the bulbous openings and the tapering teeth. This makes manufacture of the elements easier and can help to reduce stress concentrations. To compensate for the reduction of flexural stiffness a radial corrugation or rib 90 in each tooth extends past the angular transitions. In the illustrated example, the corrugations 90 complement the backing elements 52. However, the stiffening provided by the corrugations may not be necessary if backing elements are also employed.

Claims

1. A toothing element for a stripper drum, said element having a plurality of teeth each with a profile comprising a radially outwardly tapered portion and a root portion radially inwards of said tapered portion where the spacing between adjacent teeth increases to form a root opening with a maximum width greater than the radially outer neck of said opening, the element being formed in metal and the teeth having an essentially continuous rearward flange running along the edges of said profile including said root portions, and said toothing elements being arranged to be flexible yieldable transverse to said profile.

2. A toothing element according to claim 1 wherein the rearward flange is formed with an essentially constant radius junction between it and a main body of the toothing element from which it extends .

3. A toothing element according to claim 1 or claim 2 formed as a spring steel pressing.

4. A toothing element according to any one of claims 1 to 3 wherein said flexibility is increased by at least one corrugation extending transversely to the teeth in a region of the element adjacent the root opening and/or one or more apertures in said region.

5. A toothing element according to any one of the preceding claims wherein said profile edge flange is interrupted at the outer neck of each root opening.

6. A toothing element according to claim 5 wherein a stiffening corrugation or rib extends radially past said outer neck.

7. A stripper drum comprising a series of toothing elements according to any one of the preceding claims .

8. A stripper drum according to claim 7 wherein the toothing elements are arranged jointed end to end in one or more rows and a guard strip is placed in front of the elements of the or each row shielding the junctions between adjacent elements.

9. A stripper drum according to claim 7 or claim 8 when dependent on claim 5 wherein at least one guard strip overlaps a joint between successive toothing elements of a row.

10. A stripper drum according to any one of claims 7 to 9 wherein backing elements lie against the rear faces of the toothing element and have tooth-like projections with a profile that lies within the profile of the teeth of their associated toothing elements.

11. A stripper drum provided with a plurality of toothing elements each having a plurality of stripper teeth projecting from a radially innermost base portion to be held between opposed support faces of the drum by releasably clamping means passing through the base portion and said support faces, each element base portion being provided with at least one slot opening into a radially innermost edge of the element to receive said clamping means and each said toothing element having at least one locking device comprising cooperating recess and projection locking elements in the toothing element and at least one of said support faces respectively, whereby each toothing element can be put in place on the drum and be locked by sliding the element base portion between said opposed support faces while the clamping means are in position in said faces, positively in the radial direction by said recess and projection means when it is gripped between said faces by the clamping means .

12. A stripper drum according to claim 11 wherein that locking element of the or each said locking device on each toothing element is located at one or both end edges of the toothing element .

13. A stripper drum according to claim 11 or claim 12 wherein the clamping means of each toothing element is provided by a clamping device disposed centrally between a pair of said locking elements.

1 . A stripper drum according to any one of claims 11 to 13 wherein the projections and/or slots of the locking devices are formed with radiused ends.

15. A stripper drum according to any one of claims 11 to 14 wherein said support faces providing locking elements of said locking devices comprise laminar elements separable from the drum, said elements also having a means for protecting and/or stiffening the toothing elements.